Glycine-mediated inhibitory neurotransmission is essential for voluntary motor control, flex responses and sensory signal processing. The receptor for glycine is normally found in the spinal cord and the midbrain where it imparts control on motor and sensory pathways. The receptor shows selective permeability to the anion Cl− (Betz, 1991). The receptor is a pentamer of three alpha subunits and two beta subunits for a combined molecular weight of approximately 260 kDa. The channel is opened to ion flow by the binding of glycine to each of the 3 alpha subunits (Young and Snyder, 1974). The glycine receptor is effectively blocked by the compound strychnine. To date four different alpha subunits have been cloned and one beta subunit. Expression of the alpha subunits in oocytes produces a functional receptor suggesting that the alpha subunit forms the pore. The beta subunits may have modulatory roles like mediating the fast potentiation of the receptor by calcium (Fucile et al., 2000). An additional subunit, gephyrin, can associate with the intracellular region of the beta-subunit and link the receptor complex to the cytoskeleton via attachment to tubulin (Rajendra et al., 1997). The alpha subunits that have been described are comprised of approximately 420 residues. Hydropathy analysis predicts an N-terminal extracellular region, four transmembrane domains (TM1–4), and a large intracellular loop between TM3 and TM4. There are two disulfide loops on the extracellular portion of the protein that are essential for receptor function.
Mutations in the glycine receptor alpha 1 gene have been shown cause hereditary hyperkplexia and spastic paraparesis (Elmslie et al., 1996; Shiang et al., 1993). Studies on antagonists and partial agonists of the glycine receptor have suggested that the glycine receptor has a role in memory deficits in inhibitory avoidance learning (Viu et al., 2000). Other studies have shown that glycine receptors can modulated neurite outgrowth in developing mouse neurons (Tapia et al., 2000). Recent work in both mouse and hamster sperm have provided evidence for the role of glycine receptors in the acrosome reaction demonstrating that glycine receptors function outside of the nervous system (Llanos et al., 2001; Sato et al., 2000). Agonists and antagonists for these modulating factors could be useful for therapeutic purposes.
Using the above examples, it is clear the availability of a novel cloned glycine receptor alpha subunit provides an opportunity for adjunct or replacement therapy, and are useful for the identification of glycine receptor agonists, or stimulators (which might stimulate and/or bias glycine receptor function), as well as, in the identification of glycie receptor inhibitors. All of which might be therapeutically useful under different circumstances.
The present invention also relates to recombinant vectors, which include the isolated nucleic acid molecules of the present invention, and to host cells containing the recombinant vectors, as well as to methods of making such vectors and host cells, in addition to their use in the production of HGRA4 polypeptides or HGRA4sv polypeptides using recombinant techniques. Synthetic methods for producing the polypeptides and polynucleotides of the present invention are provided. Also provided are diagnostic methods for detecting diseases, disorders, and/or conditions related to the HGRA4 and HGRA4sv polypeptides and polynucleotides, and therapeutic methods for treating such diseases, disorders, and/or conditions. The invention further relates to screening methods for identifying binding partners of the polypeptides.